"The website is unacceptable, and we are improving it," one senior administration official said. "But the underlying insurance product is good, and across the country people are getting access to affordable care on January 1."

The Affordable Care Act is intended to serve more than 48 million Americans without health insurance. Most Americans face tax penalties if they do not have health insurance by January 1.

The online sign-up process began October 1 and immediately ran into technical problems. Users often were unable to create required logins and passwords and ran into error messages even after that stage. CNN's Elizabeth Cohen, who tried to enroll as an experiment, needed two weeks to reach the application stage.

Insurers also have complained of problems. Congressional hearings on the glitches are planned for next week.

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"We are going to work intensely for the next six months to make sure we meet the demand," the administration official said.

In the first release of national figures about applications, two officials told CNN on Saturday that the number of completed applications is nearly half a million, including the federal exchange serving 36 states and the state-run exchanges operating in the rest of the country.

An application is only the beginning of the process that leads to enrollment.

Applicants submit personal and financial information. After the program determines whether they are eligible for coverage and for a subsidy toward their premium costs, they can comparison shop and choose an insurance plan.

While the administration tally did not break down how many of the applications came through state-run exchanges, a CNN survey this week of officials with those exchanges found that at least 257,000 people had signed up for new insurance plans as of Friday afternoon.

Not all of them had made a payment, and not every state responded to the CNN request.

The administration has said it would release in November the number of people who have completed the enrollment process.